help im ready to sell my car.

lately i have been getting 80km when i fill up about 14.5 litres which comes up to about 20$ (canadian). I drive really slow because i have my 6 year old son in the backseat most of the time. I rarely floor it.

my specs:

2004 g35 coupe 5at 140,000km.
all stock
19" rays
K&N air filter
spark plug changed.
transmission and oil diff changed.
reset my ecu by pressing pedals
clean my throttle body
no ecu light shows up.
35psi in tires

however i have.
a tiny exhaust leak near the muffler.
last time i changed my spark plug and had some oil on it (infamous valve seal leak). my mechanic said it would be ok the spark plug is still firing. will be ok for now because the car is not sluggish and is idling fine and the oil is not affecting it because there are no ecu codes so its not misfiring, but he recommends to change it asap when i get extra money lol.

any thing i should try to improve it my gas milage?

 

80 km = about 48 miles give our take, 14.5 liters is little over 3 galons and a half. I mean youre getting about 15 miles to the galon thats not that bad given how long youve had teh car for.

 

I'm getting about 100 km out of 15L of gas..city driving

 

15mpg is not bad. i get around 17mpg with mostly highway driving at like 55-60mph. they may say the mileage is better but its never as good as they say. face it you drive a thirsty 3.5L V6 that sometimes eats gas like a V8.